1. Field of the Invention
The present invention relates generally to a touch algorithm and more specifically it relates to a touch detection using wavelet algorithm to perform signal analysis on acoustic waves that are generated by a touch on a substrate that is capable of propagating acoustic waves.
2. Description of the Related Art
Touch screens have been in use for years. Typically, touch screens are comprised of resistive, infrared, surface acoustic wave, pressure and capacitive touch screens.
The main problem with conventional resistive touch screens is the durability. After certain period of usage, the screen may fail to register certain locations. The production of resistive touch screen requires numerous manufacturing steps which include but not limited to sputtering or printing conductive coating, adding a linearization pattern and adding a cover sheet. Both resistive and capacitive products tend to loose their linearization and calibration over time. These screens can be re-calibrated by the end user; however linearization is a function of the conductive pattern and cannot be adjusted by the end user.
Infrared screens use infrared transmitters and receivers. When the screen is touched, the light from transmitter to receiver is blocked and this blockage is detected by the touch detection algorithm. The increased power consumption by infrared screens make them less likely candidate for handheld and portable applications. The increased part count of an infrared screen may reduce its reliability compared to other technologies.
Capacitive screens tend to be affected by the environmental capacitance. Therefore a system level design has to be done very carefully to make sure that not many metal objects are around the screen. This of course, increases the design and product cost. Another problem with conventional touch screens is the power consumption.
A surface acoustic screen uses more power than resistive and capacitive screens due to the fact that transmitters are always emitting acoustic waves. These screens cannot be used in handheld and portable applications due to the impact of power consumption on battery life.
recently, there are new acoustic technologies that are being developed by different companies. NXT has an acoustic wave technology that detects the “time of flight” of acoustic waves when the screen is touched. However, reflecting waves from boundaries on the screen create issue which requires absorbing material to be placed on the edges of the screen to dampen the reflective waves. This step increases manufacturing complexity. Furthermore, the signal processing unit has to be powerful enough to carry out the signal processing task which may increase the design and product cost.
A similar technology developed by Intelligent Vibrations detects the “time of flight” by using acoustic waves that are generated by a touch on the screen. This technology uses two sensors that are placed both sides of the substrate. The technology is not very sensitive to light touches. The signal processing is performed on a controller board that requires high processing power which increases the product cost.
Soundtouch Technology has an approach to characterize the screen that calculates phase differences of each point to detect the touch. The major issue with this approach is that it requires excessive amount of storage area to store the characterized data. This increases the cost of the product.
Another company called Sensitive-Object has a similar approach that characterizes the screen and stores the characterized data in the memory. Its shortcomings are the same as Soundtouch technology.
U.S. Pat. No. 5,465,302 teaches how to use an array of microphones to detect a signal coming from a speaker location. Signals detected by microphones are transformed by using Fast Fourier Transformation and the phase differences are extracted. These phase differences are used to determine the location of the speaker.
U.S. Pat. No. 6,922,642 teaches how to generate acoustic waves on a surface that is capable of transmitting acoustic waves. Furthermore, this patent teaches how to generate dispersion corrected convolution function, dispersion corrected correlation function and other phase equivalent functions to determine information related to contact on the surface.
U.S. Pat. No. 6,871,149 teaches how to use phase differences in detected signals to determine the touch location on a given surface. At least two pairs of transducers are required to detect acoustic waves generated on a surface. These signals are processed to determine the phase and then phase differences between the signals are used to determine the touch location.
WO 00/38104 World Patent Application teaches how to detect the position of a touch on a large surface. The application discusses how acoustic waves can be generated either by using a hard object or finger (either nail or skin of the finger) and then how these acoustic waves are analyzed to determine the touch location.
US Patent Application 2005/0083313 teaches how to detect the location of a touch by using phase information. This technique uses devices that can transform mechanical energy to electrical energy also known as “transducers”. Phase of the arriving signal for right and left channels are determined and then the differences between these phases are calculated and stored in a memory. When the surface is touched, phase differences between the right and the left channels are calculated and compared with the phase differences stored in the memory.
US Patent Application 2005/02127777 teaches how to characterize a surface and store the characterized data in memory. Different techniques are disclosed including how to compare measured phase differences with stored phase differences to detect the touch location.
WO0148684 teaches how to detect acoustic waves on a given surface and how to use the measured data to construct a non-dispersive signal to determine the touch location.
U.S. Pat. No. 6,456,952 teaches how to characterize a touch screen to prevent drifting.
U.S. Pat. No. 6,977,646 discloses how to do a calibration for a touch screen.
U.S. Pat. No. 5,751,276 teaches how to perform calibration on a touch screen and how to save those numbers in memory location to be used later.
U.S. Pat. No. 6,353,434 teaches how to perform calibration on a touch screen and how to store calibration data in a memory location to be used later.
U.S. Pat. No. 6,650,319 discloses complete mapping and screen characterization.
These prior art patents and patent applications reveal the fact that there is well established prior art to characterize a touch surface and store characterized information in a storage element. The stored data is compared with real time data to determine the touch location. This is pretty much the common scheme among several patents and patent applications. The amount of data storage increases as the screen size increases. In certain cases, the amount of data may be a prohibiting factor for product implementation and in other cases, it increases the product cost. Therefore the ability of using a new technique to reduce the amount of data to be stored is highly desired.
In these respects, the touch detection using wavelet algorithm according to the present invention substantially departs from the conventional concepts and designs of the prior art, and in so doing provides an apparatus primarily developed for the purpose of detection of a touch on a given surface by receiving acoustic waves generated by a touch and performing signal analysis on these acoustic waves using wavelet transformation such that data storage requirement is substantially reduced.